'\" et
.TH sys_un.h "0P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
sys/un.h
\(em definitions for UNIX domain sockets
.SH SYNOPSIS
.LP
.nf
#include <sys/un.h>
.fi
.SH DESCRIPTION
The
.IR <sys/un.h> 
header shall define the
.BR sockaddr_un
structure, which shall include at least the following members:
.sp
.RS 4
.nf

sa_family_t  sun_family  \fRAddress family.\fR
char         sun_path[]  \fRSocket pathname.\fR
.fi
.P
.RE
.P
The
.BR sockaddr_un
structure is used to store addresses for UNIX domain sockets.
Pointers to this type shall be cast by applications to
.BR "struct sockaddr *"
for use with socket functions.
.P
The
.IR <sys/un.h> 
header shall define the
.BR sa_family_t
type as described in
.IR <sys/socket.h> .
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
The size of
.IR sun_path
has intentionally been left undefined. This is because different
implementations use different sizes. For example, 4.3 BSD uses a size of
108, and 4.4 BSD uses a size of 104. Since most implementations
originate from BSD versions, the size is typically in the range 92 to
108.
.P
Applications should not assume a particular length for
.IR sun_path
or assume that it can hold
{_POSIX_PATH_MAX}
bytes (256).
.P
Although applications are required to initialize all members
(including any non-standard ones) of a
.BR sockaddr_in6
structure (see
.IR "\fB<netinet_in.h>\fP"),
the same is not required for the
.BR sockaddr_un
structure, since historically many applications only initialized
the standard members. Despite this, applications are encouraged
to initialize
.BR sockaddr_un
structures in a manner similar to the required initialization of
.BR sockaddr_in6
structures.
.SH "RATIONALE"
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fB<netinet_in.h>\fP",
.IR "\fB<sys_socket.h>\fP"
.P
The System Interfaces volume of POSIX.1\(hy2017,
.IR "\fIbind\fR\^(\|)",
.IR "\fIsocket\fR\^(\|)",
.IR "\fIsocketpair\fR\^(\|)"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
